Fuel cells are now being used in vehicles and in other fields. In a solid polymer fuel cell (hereafter simply referred to as a “fuel cell”), an assembly (MEA: Membrane Electrode Assembly) comprising an electrolyte film formed from a solid polymer film sandwiched between two electrodes, namely a fuel electrode and an air electrode, is itself sandwiched between two separators to generate a cell that functions as the smallest unit, and a plurality of these cells are then stacked to form a fuel cell stack (FC stack), enabling a high voltage to be obtained.
Here, the fuel cell separators are formed from a metal material such as SUS. A multitude of techniques have been proposed for improving the corrosion resistance of the separators formed from this metal. For example, JP 2002-25574 A and JP 2005-158441 A disclose a technique in which the peripheral edges of the separator manifold are covered with a resin or film having excellent corrosion resistance. The manifold describes an aperture formed in the separator, and the fuel gas, air and moisture and the like pass through this manifold.
However, the surface of the separator is normally coated with a chemically inert passivation film, and the bonding strength to resins or the like is weak. As a result, the stress generated during cell stacking, and the stress generated due to the expansion that occurs under the action of the heat generated during operation of the fuel cell may cause the resin layer or the like to peel. Furthermore, because the surface of the separator has inherently poor wetting properties, if the resin coating material is water-soluble, then applying the resin coating material uniformly to the separator surface is impossible, and a favorable resin layer can not be formed.
JP 2000-243408 A discloses that when those regions of the fuel gas passages formed within the center of the separator that do not contact the electrode are coated with a resin, the bonding properties with the separator can be improved by including OH groups within the resin. Furthermore, JP 2003-272655 A discloses a technique in which a passivation treatment is conducted by immersing the separator in an acidic bath in order to improve the performance of the fuel gas passages. However, both of these techniques aim to improve the quality and function of the fuel gas passages, and applying these techniques to improvement of the quality and function of those regions of the separator besides the gas passages is problematic.
In other words, with the conventional technology, effectively improving the corrosion resistance and the like of those regions of the separator besides the gas passages is problematic, and as a result, improving the quality of the fuel cell itself is difficult.
Accordingly, it is an advantage of the present invention to provide a separator that is capable of improving the quality of a fuel cell, and a process for producing the separator.